Simple frictional weld

ABSTRACT

A cooling channel piston for an internal combustion engine which includes a piston bottom and a piston shaft that are joined thereto of a friction welding process. The piston bottom and the piston shaft jointly form a cooling channel. An annular wall which radially delimits the cooling channel towards the outside is formed by the piston bottom and/or the piston shaft. The annular wall can be sealed by a welding process once the piston bottom and the piston shaft have been joined together.

The invention relates to a one-piece, steel welded cooling-channelpiston of forged steel in accordance with the features of the preambleof claim 1.

The object of the invention is to develop a piston surpassing the priorart in which the cooling channel or cooling cavity is tightly sealed. Apiston of this type is described, for example, in the unpublished Germanpatent application DE 10 2004 038 465.7.

A cooling channel piston is known from the previously published Germanpatent application DE 102 44 512 A1 having the features which constitutethe genre. The upper part of the piston has circumferential radial websrunning coaxially behind the ring belt which are joined to correspondingwebs on the piston skirt by means of friction welding. After the joiningof piston upper part and piston lower part, the lower face of the ringbelt is located adjacent the upper circumferential radial face of thepiston skirt. In the state when piston upper and lower parts are joined,the outer piston wall areas between both parts of the piston form acontact surface which is characterized by a gap a few tenths of amillimeter wide. It can remain open or be sealed by means of atemperature-resistant sealing ring which is positioned before thejoining of both parts of the piston on one of the contact surfaces, forexample that of the lower part of the piston. A sealing ring of thiskind has the advantage that the cooling channel is then closed to form aseal, but in a disadvantageous manner it represents an additionalcomponent which has to be produced and correctly positioned when the twoparts of the piston are joined. In addition, the sealing ring, just likethe few tenths of a millimeter wide gap without a sealing ring, has thedisadvantage that the upper part of the piston (piston crown) cannot besupported on the lower part of the piston (piston skirt) while thepiston is operating. While operating, the piston crown is deformed in adisadvantageous manner by the combustion pressures acting on it so thatthe strength and durability of the piston are compromised.

A cooling channel piston for a combustion engine is known from EP-A-1061 249, having a piston crown and a piston skirt joined by means offriction welding, which together form a cooling channel, where a ringwall delimiting the cooling channel radially outward is formed by thepiston crown and/or the piston skirt and the ring wall can be closed toform a seal by an interference fit and/or positive fit after pistoncrown and piston skirt have been joined. As shown in FIGS. 2 to 5, thesurfaces of the ring belt and of the piston skirt facing each other areradially circumferential and coplanar with each other. The mutuallycoplanar facing surfaces on the lower edge of the ring belt and theupper edge of the piston skirt do not have any type of shoulder so thatwhen the cooling channel piston is operating, there is no adequatesupport for the piston crown on the piston skirt. Only in FIG. 6 is itshown that the upwardly facing termination of the piston skirt has asingle shoulder with which the coplanar aligned lower part of the ringbelt can come into contact. This certainly improves the supportingeffect, but not optimally. In addition, the inwardly directed L-shape ofthe shoulder at the upper end of the piston skirt is extremely difficultand expensive to manufacture with the required precision, so that nopractical solution can be derived from EP-A-1 061 249.

Generic cooling channel pistons are also known from US 2004/144247 A1and US-B1-6698391 in which, however, the circumferential radial loweredge of the ring belt and the upper edge of the piston skirt coming intocontact therewith are also only configured coplanar so that thesupporting effect is not disclosed.

The object of the invention is therefore to prepare a cooling channelpiston which effectively avoids the disadvantages described initially.

The object of the invention is achieved to the extent that the upper andlower part of the cooling channel steel piston are first joined by meansof friction welding or resistance press welding where a ring walldelimiting the cooling channel in an outward direction does notinitially form a material bond and the tight sealing of the ring wall ofthe cooling channel is achieved by means of an interference and/orpositive fit, specifically a subsequent welding process. An advantageousjoining and closing of the cooling channel is now possible through thedesign of the cooling channel piston in accordance with the invention,wherein the joined parts, that is, piston crown and piston skirt, arejoined by means of friction welding or resistance press welding. Thesubsequent external welding (not friction welding), or the correspondingshaping of the ring wall respectively, affects the cooling channel tothe extent that no flashes from friction welding extend into the coolingchannel in the area of the ring wall. Through the subsequent welding ofthe outer ring wall, or generally through the interference and/orpositive fit, the piston is supported in the area of the ring belt, thatis, the forces acting on the piston crown can be transferred to thepiston skirt, which considerably increases the strength and durabilityof the cooling channel piston. At the same time, the welding alsocounteracts deformation in the skirt area, particularly in its upperarea. In addition, manufacturing tolerances between the upper and lowerpart are compensated. In addition, provision is made in accordance withthe invention for both the face of the ring wall below the ring belt andalso the adjoining face of the ring side above the piston skirt to havea matching shoulder. As a result, both in the case of the interferencefit and in the case of the positive fit connection the cooling channelis dosed and the support of the piston crown on the piston skirt isoptimized in the contact or joint area.

Additional welded-in parts can be dispensed with due to the piston beingformed only of piston crown and piston skirt, which considerablysimplifies the manufacture of a cooling channel piston in accordancewith the invention. Additionally, one advantage of the invention isthat, depending on the configuration of the joint area around the ringwall, this joint area can serve to lend rigidity to and position thejoined parts during the friction welding. A cost saving results at thesame time because welded-in parts can be dispensed with in the area ofthe cooling channel.

The invention will be described hereinafter with reference to anembodiment to which the invention is not restricted and explained by theFIGS. 1 to 4.

FIG. 1 shows the section through a one-piece, welded cooling channelpiston, specifically of forged steel.

One half of a sectioned view of a piston and specifically of a coolingchannel piston for a combustion engine is shown In FIG. 1. The coolingchannel piston 1 shown here consists of a piston crown 2 and a pistonskirt 3 which are joined by means of friction welding which results in afriction welding seam 4. The piston crown 2 is formed from a combustionbowl 5, an upper land 6, a ring belt 7 and one part of a cooling channel8. The area of the piston skirt 3 comprises an outer skirt surface 9 ofthe cooling channel piston 1, a piston pin bore 10 and a lower part 11of the cooling channel. The cooling channel 8 is consequently formed ofan upper and a lower area 11 of the piston crown 2 and the piston skirt3 and a recessed, circumferential web of the piston crown 2 and thepiston skirt 3.

In this embodiment an additional groove 12 is introduced into the outersurface of the piston 1 below the ring belt 7. After the piston crown 2and the piston skirt 3 have been joined by friction welding, the twoparts of the piston 2, 3 merely abut each other in the area of the ringwall 13 without the existence of a material bond and/or tight connectionin the area of this ring wall 13. The joining of the ring wall 13 iscarried out in a subsequent, supplementary welding process. Here, thewidest variety of welding processes (but not friction welding), such asfor example, electron beam welding, WIG welding, MIG welding, MAGwelding, laser welding, etc. is conceivable.

In this embodiment, a shoulder 14 is incorporated in the joint area ofthe ring wall 13 which has the advantage that when welding the ring wall13, the weld seam root does not extend into the cooling channel 8 and inaddition, a tight weld is made possible by welding up the shoulder and aclean, pore-free root is created.

The design of the shoulder 14 is not restricted to this embodiment, butrather the creation of other shoulder shapes 14 in the area of the ringwall 13 is conceivable which either assist the subsequent weldingprocess or have a positive effect on the friction welding.

An additional advantage of welding the ring wall 13 afterwards is thatuntil immediately before the final joining of the piston crown 2 and thepiston skirt 3, inert gases can penetrate through the gap in the ringwall 13 into the area of the friction weld seam which in turn have apositive effect on the material structure in the friction weld seam 4.The location of the shoulder 14 in the area of the ring wall 13 isplaced exactly in the center of the groove 12 only as an example. Thisshoulder 14 lies advantageously below the ring belt 7 and above thelower end 15 of the cooling piston channel. It is also conceivable inaccordance with the invention not to introduce a groove 12 into thepiston 1 and to form the ring wall 13 only with the surface of the skirt9.

With a view to FIG. 1, it should be pointed out once more that the ringwall 13 is formed by the lower face of the ring belt 7 and the uppershoulder of the piston skirt 3. Because of the geometry in the area ofthe ring wall 13 shown in FIG. 1, the welding procedure can be performedparticularly conveniently. The matching shoulders of the opposing faces,as already explained, prevent the weld seam from forming towards thecooling channel 8. Besides that, the advantage of the welding process tobe performed radially on the outside remains, specifically that the weldseam projecting radially outward can be removed, for example bymachining. In addition to this ring wall 13 geometry shown in FIG. 1, itis also conceivable that the upper part of the piston skirt 3 has aplateau which the lower face of the ring belt 7 contacts after thefriction welding process. It is also conceivable that the ring belt 7 islocated on the piston skirt and comes into contact with a lower facebelow the upper land 6. The advantages described initially remain withthese geometries as well. The basic principle of the present inventionis important and advantageous, namely that) that the piston crown 2 andthe piston skirt 3 have webs recessed from the outer surface runningradially circumferential which are joined by means of friction weldingwhile the ring wall 13, which is shaped so that the faces of the ringwall 13 bordering each other (of the piston crown 2 and/or of the pistonskirt 3) do not yet form a material joint in the friction weldingprocess, is directly on the outer surface of the cooling channel piston1. The welding of the adjacent faces of the ring wall 13 takes place inan additional step from the outside only after piston crown 2 and pistonskirt 3 have been joined through their internal webs by means offriction welding.

FIG. 2 shows the area of the ring wall 13 where the part of the face ofthe ring belt 7 projecting downward is configured in a grooved shapeinto which a radially circumferential shoulder facing upwards engagesabove the face of the piston skirt 9. Here too, welding the adjacentfaces of the ring wall 13 is subsequently carried out from the outside.This closes the cooling channel 8 completely, the ring belt 7 issupported against deformation when the cooling channel piston 1 isoperating, and the piston skirt is supported against deformation, inparticular in the upper area.

FIG. 3 shows a section of the area of the ring wall 13 where the lowercircumferential section of the ring belt 7 and the upper circumferentialsection of the piston skirt 9 are shown. In the design in accordancewith FIG. 3, the face of the ring wall 13 below the ring belt 7 and theadjacent face of the ring side 13 above the piston skirt 9 areconfigured in the manner of a groove, similar to FIG. 2, but with theparticular feature that the circumferential tongue 17 has a height Xwhich is greater than the depth Y of the groove 16. The procedure duringmanufacture of the cooling channel piston 1 is that piston crown 2 andpiston skirt 3, as already described, are joined by means of frictionwelding or resistance press welding and thereby the two faces of thering wall 13 from FIG. 3 (are at a distance (with a gap) and do notcontact each other. Subsequently the cooling channel piston 1 is pressedtogether from above and from below, in the axial direction of the pistonstroke. The opposed faces of the underside of the ring belt 7 and of theupper side of the piston skirt 9 come into contact, where simultaneouslythe radially circumferential tongue 17 is deformed inside the radiallycircumferential groove 16 so that an interference fit and a positive fitresult in the area of the ring wall 13, which ensures that the coolingchannel 8 is closed to form a seal and at the same time the piston crown2 can rest on the piston skirt 9. In a preferred embodiment, thisinterference and positive fit is sufficient, although it is alsoconceivable to reinforce the contact area additionally in the area ofthe ring wall 13 through a material bond by means of a weldingprocedure.

Something similar applies in the embodiment in accordance with FIG. 4,where the face of the ring wall 13 below the ring belt 7 and theadjacent face of the ring side 13 above the piston skirt 9 both have amatching shoulder. In this instance also, the opposing faces are not ininitial contact after the piston crown 2 and piston skirt 3 have beenjoined, but a gap has formed instead. To eliminate the gap to achievesealing of the cooling channel 8 and absorption of force for the pistoncrown 2 on the piston skirt 3, the cooling channel piston 1 is againexposed to a force from above and from below so that in the area of thecontact surfaces an interference or a positive fit results. The coolingchannel 8 is sealed and absorption of force is provided so that incontrast to the embodiment from FIG. 1, a welding procedure in the areaof the ring wall 13 can be omitted.

In summary, it must be pointed out once again that initially the pistoncrown 2 is joined to the piston skirt 3 by means of friction welding orresistance press welding. This joining takes place in an area clearlyset back from the ring belt 7 which is located coaxially between theback side of the ring belt 7 and the outer circumference of thecombustion bowl 5 to achieve sufficient rigidity. Following this joiningof piston crown 2 and piston skirt 3, the ring wall 13 (the area belowthe ring belt 7 and above the piston skirt 9) is closed by means of aninterference and/or positive fit such that on the one hand the coolingchannel 8 is sealed and on the other hand the piston crown 2 can rest onthe piston skirt 3 in such a way that deformation of the piston crown 2when the cooling channel piston 1 is operating is clearly reduced sincethe combustion pressures or forces acting on the piston crown 2 can betransferred to the piston skirt (9). In this case the contact area inthe region of the ring wall 13 can still be materially joined by meansof a welding process, but this can normally be dispensed with.

Alternatively, or additionally, the geometric relationships after thejoining of piston crown 2 and piston skirt 3 are such that the facesbelow the ring belt 7 and above the piston skirt 9 are not yet incontact, but a gap has formed. In order to seal the cooling channel 8and to ensure the absorption of forces from the piston crown 2 to thepiston skirt 3, this area of the ring wall 13 is closed in a manner inaccordance with the invention as a positive fit by means of a weldingprocedure, as already described. The opposing faces can be configuredplanar or be configured from other geometric shapes (as for examplestep-shaped in accordance with FIG. 3 or tongue-and-groove as in FIG. 3.

With reference to FIG. 1, it must be pointed out supplementary that inthe internal region of the cooling channel piston 1 there may be, butdoes not have to be, an additional, radially circumferential web 18.This web 18, which can be manufactured with the cooling channel piston 1or as a separate component which can be joined to the cooling channelpiston 1, then forms at least one further cooling channel 19, where inaddition to the two cooling channels 8, 19, which can also be describedas cooling chambers, a cooling medium can be introduced centrally in theinterior area of the cooling channel piston 1, permanently orcirculating. Not shown, but present, are on the one hand means withwhich the cooling medium can be sprayed into the cooling channel orcooling channels, and on the other hand the necessary orifices, as forexample holes on the underside of the interior area or also inside thewebs separating the cooling channels.

REFERENCE NUMERAL LIST

-   -   1. Cooling channel piston    -   2. Piston crown    -   3. Piston skirt    -   4. Friction welding seam    -   5. Combustion bowl    -   6. Top land    -   7. Ring belt    -   8. Cooling channel    -   9. Skirt surface    -   10. Piston pin hole    -   11. Lower area    -   12. Groove    -   13. Ring wall    -   14. Shoulder    -   15. Lower end    -   16. Groove    -   17. Tongue    -   18. Web    -   19. Cooling channel

1. The cooling channel piston for a combustion engine, comprising: apiston crown and a piston skirt attached thereto by means of a weldwhich together form a cooling channel: a ring wall delimiting thecooling channel radially outward at least formed by one of the pistoncrown or the piston skirt and the ring wall closed to form a seal by oneof an interference and a positive fit after piston crown and pistonskirt have been joined; and a face of the ring wall below a ring beltand an adjoining face of a ring side above the piston skirt both have amatching shoulder.
 2. The cooling channel piston of claim 1, wherein thering wall is closed to form a positive fit by means of a another weld.3. The cooling channel piston claim 1 wherein the face of the ring wallbelow the ring belt and the adjacent face of the ring side above thepiston skirt are configured in the shape of a groove.
 4. The coolingchannel piston of claim 3, wherein a circumferential groove in the lowerface of the ring belt has a lesser depth (X) than a circumferentialtongue has height (Y), the tongue (17) being deformable after the pistoncrown and piston skirt have been joined.
 5. The cooling channel pistonof claim 1 wherein in an inner area of the cooling channel piston atleast one additional, radially circumferential web is disposed to format least one additional cooling channel.
 6. The cooling channel pistonof claim 1, where the weld is one of a friction weld and a resistanceweld.
 7. The cooling channel piston of claim 2, wherein the another weldis a non-friction weld.
 8. The cooling channel of claim 1, wherein theface of the ring wall below the ring belt and the adjacent face of thering side above the piston skirt have matching grooves.